1. FIELD OF THE INVENTION
This invention relates to heat pump systems which employ a multiple slide valve helical screw compressor and more particularly to such a system which cascades an air source heat pump through a two-pipe arrangement to a closed loop of circulating liquid such as water, employing individual water to air heat pumps for zone heating of a building to be conditioned.
Applicant's U.S. Pat. No. 3,936,239 and applicant's copending application Ser. No. 653,568 now U.S. Pat. No. 4,058,988 employ a helical screw rotary compressor within a heat pump, heating and cooling refrigeration system wherein the compressor employs multiple, axially shiftable slide valves for; controlling the capacity of the compressor, matching the closed thread pressure of the compressor at discharge to discharge line pressure, controlling the point of injection of a refrigerant gas return from a subcooling or economizer coil, or a high pressure evaporator coil to a point within the compression process which is at a higher pressure than the suction pressure of the compressor and at a lower pressure than the discharge pressure of the compressor, and axially adjusting the point of compressed working fluid vapor removal for feeding a secondary closed refrigeration loop at a pressure less than that of full compressor discharge.
The heat pump heating and cooling system, particularly within the copending application, is provided with an air source evaporator/air cooled condenser coil positioned exterior of the building to be conditioned and which advantageously employs that coil as a source of thermal energy for heating the building, particularly by way of hydronic system heating condenser within the building and within the closed loop including the compressor and the air source evaporator/air cooled condenser coil.
In both that application and the present application, the helical screw rotary compressor incorporates a number of longitudinally shiftable slide valves which preferably consist of a suction or capacity control slide valve, a pressure matching or discharge slide valve, an injection slide valve for injecting vapor into the compressor at a point of the compression process intermediate of the compressor suction and discharge pressures and an ejection port for removing from the compressor partially compressed refrigerant vapor for feeding refrigerant through a secondary loop constituting a lower pressure heat exchanger.